U.S. patent number 7,347,507 [Application Number 11/656,207] was granted by the patent office on 2008-03-25 for brake controller.
Invention is credited to Ralph Stillinger.
United States Patent |
7,347,507 |
Stillinger |
March 25, 2008 |
Brake controller
Abstract
Brake controller for controlling the brakes of a towed vehicle
is provided. The controller includes microprocessor, an
accelerometer, a storage array for storing a sequence of signals,
and associated software for computing a moving average of
accelerometer values thereby providing data on which the braking
requirements of the towed vehicle can be determined. Feedback based
on the power consumed during the braking event is likewise utilized
to modify the power delivered to the braking system during
subsequent braking events.
Inventors: |
Stillinger; Ralph (Plano,
TX) |
Family
ID: |
39199157 |
Appl.
No.: |
11/656,207 |
Filed: |
January 22, 2007 |
Current U.S.
Class: |
303/7; 303/20;
701/70 |
Current CPC
Class: |
B60T
7/20 (20130101); B60T 8/1708 (20130101); B60T
8/24 (20130101); B60T 2201/04 (20130101) |
Current International
Class: |
G06F
7/70 (20060101) |
Field of
Search: |
;188/1.11E,1.11L
;303/7,20 ;701/70 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schwartz; Christopher P.
Attorney, Agent or Firm: Young Basile
Claims
The invention claimed is:
1. A brake controller for operating the brakes of a vehicle
comprising: A microprocessor; An accelerometer; Means for
generating a sequence of signals utilizing said accelerometer prior
to operating said brakes; A storage array for storing said sequence
of signals generated by said accelerometer; Means for averaging
values stored in said array; Means for generating an output; and
Means for applying braking to said vehicle based on said
output.
2. A method of applying brakes to a vehicle comprising the steps
of: providing a brake controller, said brake controller including
an accelerometer; generating a sequence of signals utilizing said
accelerometer prior to operating said brakes; transferring values
from said accelerometer to a storage array; computing a moving
average of the values of said storage array; computing braking
signals by a microprocessor based on said moving average; and
activating the brakes of said vehicle in response to said signals
provided by said microprocessor.
3. A method of automatically maintaining consistent braking
utilizing measured feedback based on braking frequency, vehicle
inclination and amperage measurements to correct brake fade,
comprising: providing a brake controller, said brake controller
including an accelerometer; generating a sequence of values
utilizing said accelerometer prior to operating said brakes:
transferring values from said accelerometer to a storage array;
computing a moving average of the values of said storage array;
computing braking signals utilizing a microprocessor, based on said
moving average; adjusting said braking signals based on one or more
of said braking frequency, said vehicle inclination and said
amperage measurements; and activating the brakes of said vehicle in
response to said signals provided by said microprocessor and said
amperage measurements.
Description
FIELD OF THE INVENTION
The present invention pertains to brake controllers, and, more
specifically, to controllers for applying selected amounts of power
to the brakes of a vehicle.
BACKGROUND OF THE INVENTION
A wide variety of vehicles utilize electronic brakes. While these
types of vehicle are typically of the class of towed vehicles such
as trailers, in certain instances self-powered vehicles may also be
provided with electronic brakes. Regardless, however, of whether or
not the vehicle is independently operated, operating as a towing
vehicle, or operating as a towed vehicle, the application of brakes
to that vehicle dictates a consideration of a vehicle's speed,
forward or rearward acceleration or deceleration, lateral
acceleration or deceleration, as well as the angle, in relation to
the horizontal, on which the vehicle may be operating, such as when
climbing or descending a hill or other incline.
Brake controllers may be manufactured as a part of the vehicle, or
may be independently manufactured and installed in the vehicle as
an after-market item. In either event, the function of the brake
controller is to apply a suitable amount of braking power to
electronic brakes to insure a smooth, safe and controlled stop.
There are a number of problems with existing brake controllers. For
example, after-market brake controllers are typically installed in
cars, light trucks, or other towing vehicles to provide a braking
signal to a trailer being towed by the towing vehicle and attached
to the towing vehicle by a trailer hitch or similar mechanical
attachment. For very light towed vehicles, it is possible and
acceptable to dispense with a separate braking system for the towed
vehicle, and, in fact, many lightweight trailers currently in use
have no brakes of any kind. However, once the weight of the towed
vehicle becomes more substantial, it is desirable to provide the
towed vehicle with a separate braking system. While such systems
may be hydraulic, pneumatic or electrical, it is generally accepted
that electrical braking systems are the most desirable, inasmuch as
they are simple to interface with the braking system of the towing
vehicle.
In its simplest form, the brake controller used in this environment
is a relay or switch which senses the operation of the brakes in
the towing vehicle, and thereupon applies braking power to the
towed vehicle. Often the controller senses a signal from the towing
vehicle by virtue of the fact that the towing vehicle's brakes are
operated simultaneously with the towing vehicle's brake lights. By
connecting the towing vehicle's brake light circuit to the
controller, the controller can be made to operate, and hence send a
braking signal to the towed vehicle, whenever the brake lights of
the towing vehicle are activated.
Unfortunately, such simple systems are entirely unsuitable for
operation in a modern traffic system. It is undesirable that the
towed vehicle's brakes be fully applied whenever the towing
vehicle's brake light circuit is activated. Under these
circumstances, the towed vehicle's fully applied brakes will
essentially lock the towed vehicle's wheels, providing
substantially more braking than is required and placing enormous
stress on the mechanical connection between the towed and the
towing vehicle.
It is essential, therefore, that the braking power being applied to
the towed vehicle's brakes be proportional to the braking power
applied to the towing vehicle's brakes and that the amount of
braking power so provided be fully variable. Accordingly, just as
an increase in pressure on the brake pedal of a motor vehicle
having hydraulic brakes results in gradually increasing braking
forces, so must a variable amount of braking power be applied to
the electric brakes of the towed vehicle to insure a smooth and
safe stop or deceleration.
Fortunately, electrical brakes installed on most towed vehicles are
well suited to fully proportional operation. Since the electronic
actuators in electronic brakes are capable of providing braking
force proportional to the amount of electrical energy supplied,
techniques and equipment have been developed to permit the gradual
application and gradual release of braking forces to the electronic
brakes of such vehicles.
One simple approach has been to provide a control device, such as a
potentiometer, which applies a proportional amount of braking to a
vehicle's electronic brakes depending on the position of the
potentiometer over its range. For such a device to work
effectively, however, it is essential that the potentiometer or
other variable control be interconnected with the pneumatic or
hydraulic brakes of a towing vehicle. Such interconnection requires
substantial engineering and assembly effort, and is difficult to
accomplish as a retrofit or after-market product. Further, while
currently known brake controllers sometimes have such a variable
control which can be manually operated, it is difficult to
simultaneously apply braking to the towing vehicle (for example,
with the foot of the operator), and to achieve comparable
proportional braking to the towed vehicle (for example, with the
hand of the operator), by operating a manual control on a separate
controller device. Inevitably, in these circumstances, either too
little or too much braking energy is applied to the brakes of the
towed vehicle.
To overcome these problems, modern brake controllers often include
a mechanical accelerometer which senses the amount of deceleration
of the towing vehicle and applies electrical energy to the brakes
of the towed vehicle in an amount proportional to the deceleration
of the towing vehicle. In a non-abrupt, mild stop situation, where
the towing vehicle may take a long distance to bring the combined
towing/towed vehicle to a stop, the accelerometer would sense very
little deceleration and apply little or no electrical energy to the
brakes of the towed vehicle. By contrast, in an emergency stop
situation, the accelerometer senses that the towing vehicle is
making an abrupt stop, and accordingly the controller will apply a
proportionally higher amount of electrical energy to the brakes of
the towed vehicle. While this type of controller is a substantial
improvement over the earlier and more primitive controllers, these
controllers still tend to under-apply and over-apply forces during
braking actions.
The inability of this type of controller to accurately measure
acceleration and deceleration is a function of reliance on simple
mechanical accelerometers. Presently, brake controllers do not
compensate for resistive changes due to heat and the frequency of
brake use. The amount of braking required by a vehicle in city
driving, characterized by frequent starts and stops, is very
different than that required by the same vehicle travel in a
highway setting where there are fewer braking events. Further,
these controllers are typically capable of measuring only straight
line acceleration and/or deceleration, and do not sense or respond
to lateral acceleration. Additionally, these controllers are not
provided with the ability to sense the inclination of the towing
vehicle, i.e., whether the towing vehicle is ascending or
descending an incline. The amount of braking energy required to
slow a vehicle moving up an incline is substantially less than that
required of the same vehicle on level ground. Conversely, the
amount of braking energy required for a vehicle descending an
incline is substantially higher than that required for a vehicle
decelerating on level ground. Finally, this type of controller
operates in a temporally limited manner, i.e., it does not store
and analyze data regarding vehicle movement and inclination.
Recently brake controllers have been developed which overcome some
of these difficulties by using modern multi-axis solid state
accelerometers. Robinson, et al., in U.S. Pat. No. 6,837,551,
teaches the use of a multi-axis accelerometer in association with a
microprocessor to supply braking to a towed vehicle in response to
precisely measured acceleration forces in more than one axis. This
device, however, uses polling techniques which do not provide
enough acceleration data to assure smooth braking. Substantial
improvements can be made to the existing art through improved
algorithms for analysis of the accelerometer data, specifically by
incorporating historical information regarding a towing vehicle's
movement in advance of brake operation. By continuously monitoring
the acceleration and orientation of the towing vehicle, more
effective braking of the towed vehicle can be achieved.
Current controllers provide only limited feedback to the operator
as to the condition of the brake controller itself, and the
functionality of the brake controller both before and during the
braking operation. The present invention provides an alphanumeric
and graphical display for providing substantial feedback to the
vehicle operator about the braking system.
It is an object of the present invention to provide a means to
control the brakes of a vehicle by continuously compiling data
regarding the movement and orientation of the vehicle in advance of
a braking event.
It is another object of the present invention to provide a brake
control device that accurately measures acceleration, deceleration
and orientation of a vehicle without reliance on mechanical
inputs.
It is further an object of the present invention to provide a
controller which provides substantial information to the operator
of a towing vehicle regarding the operation of the brake
controller.
It is a further object of the present invention to provide a brake
system controller which is easily operated by a person in a towing
vehicle without the need for manipulation of mechanical
controls.
It is a further object of the present invention to provide a brake
controller for use in a towing vehicle that assures that the brakes
of a towed vehicle are operated accurately and proportionally to
the amount of braking energy required in view of the deceleration
and/or orientation of the towing vehicle, both automatically, and
through manual means.
It is a further object of the present invention to provide a brake
controller which does not rely on mechanical inputs such as
pneumatic and hydraulic sensors, but which provide superior braking
through emulation of this type of mechanical input by simulating
those inputs utilizing electronic hardware and software.
It is a further object of the present invention to provide a brake
controller that automatically compensates for resistive changes in
the braking environment, including heat or other resistive changes
to the electrical braking system.
Other objects and advantages of the present invention will be
apparent from the following description.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is a brake
controller which may be included as part of the original equipment
in a towing vehicle, or provided as an after-market device. The
controller is preferably provided with an enclosure, one or more
mounting means, and one or more manually operable controls, as well
as electrical connection means to permit the controller to be
secured in a convenient location within the vehicle, and
electrically connectable to the electrical circuits of the vehicle,
and to any towed vehicle associated with the vehicle. The
operational components of the controller are preferably contained
on one or more printed circuit boards which carry a number of
electrical components which will be explained in further detail
herein.
In the preferred embodiment of the invention, the controller is
mounted in such a location to insure that the controls are easily
within reach of the vehicle operator, and so that the display
provided on the controller is easily visible to the vehicle
operator. The controller enclosure may be designed to be mounted to
the dashboard, steering column, console, or other easily accessible
element in the interior of the motor vehicle, including mounting in
the instrument panel itself for both aesthetics and convenience of
operation.
In the described embodiment, the controller is provided with a
integral power supply which connects to the electrical power source
of the vehicle in which the controller is mounted. The power supply
serves to condition the electrical power from a vehicle in which
the controller is mounted to insure a reliable source of electrical
energy at the various voltages required by the electrical brake
actuators, the brake lights, and the controller circuits
themselves. In this fashion, reliable electrical voltage and
electrical current parameters are maintained during operation of
the controller.
The controller of the present invention utilizes a microcontroller
which accepts inputs from an accelerometer, stores those inputs,
and subsequently utilizes those inputs to provide a conditioned
power output for operating the brakes of the towed vehicle. A
customized algorithm provides electronic braking signals to the
towed vehicle which emulate the braking power of a typical
hydraulic brake, utilizing the accelerometer data. The controller
also includes a full function display, which provides visual
signals of the condition and operation of the controller.
Manual braking inputs are also available to the vehicle operator,
and the controller provides to the operator substantial data
regarding the braking event.
DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view of a controller according to an
illustrated embodiment of the present invention.
FIG. 1A is a perspective view of a controller according to the
present invention as installed in a motor vehicle.
FIG. 2 is a block diagram of the various components of the
controller showing interconnection between the controller and a
towing and towed vehicle.
FIG. 3 is a schematic of the controller power supply.
FIG. 4 is a schematic of the brake switching circuitry of the
controller.
FIG. 5 is a schematic of the brake light circuitry.
FIG. 5A is a schematic of the signals interface circuitry.
FIG. 6 is a schematic of the microprocessor and microprocessor
interface to the components of the controller.
FIG. 7 is a flow chart of the main process loop software for
operation of the controller.
FIG. 8 is a flow chart of the brake action software utilized by the
controller.
FIG. 9 is a chart depicting the raw and extrapolated accelerometer
readings compared to the hydraulic pressure per square inch being
produced by the hydraulic braking system of the towing vehicle.
FIGS. 10-12 are depictions of various pulse width modulated braking
signals.
DESCRIPTION OF PREFERRED EMBODIMENT
As depicted in FIG. 1 and FIG. 1A, the invention is a controller 10
which includes a case 2 which houses all of the electrical
components, and features a lens 3 through which the display herein
described may be visualized. The case 2 is further provided with a
plurality of switches 4A, 4B and 4C which control the various
functions of the invention as herein described. Electrical
connections between the controller 10 and the vehicle in which it
is mounted are made through a series of electrical conductors
housed within an umbilical sheath 5 which provides protection for
the electrical conductors and presents a neat, aesthetically
pleasing configuration. The controller 10 also includes a manual
switch 6, whereby a manual braking signal can be sent directly from
the controller 10 to the vehicle braking system. Preferably, manual
switch 6 is in the form of a spring-loaded, linear potentiometer
which allows the switch to be easily operated over a range of
motion by the hand of the vehicle operator. The controller 10 also
features an enunciator window 7, typically housing a light emitting
diode, which provides a power indication when the controller is
generating a braking command.
To facilitate mounting of the controller 10 on a vehicle dashboard
12, the controller case 2 is provided with a bracket 8 and a pair
of thumbscrews 9. This commonly used mounting arrangement provides
substantial versatility for the controller 10 by simplifying the
mounting of the controller 10 on the vehicle dashboard 12, and
permitting the controller case 2 to be pivoted upward and downward
so that the lens 3 of the case 2 is easily visible to the operator
of the vehicle.
The invention and its operation will be further understood by
referring to FIG. 2, a block diagram of the various components of
the controller 10 showing interconnection between the controller 10
and a towing and a towed vehicle. The controller 10 comprises a
microprocessor circuit 20, power supply circuit 100 and
accelerometer circuit 200, a keypad circuit 300, a display circuit
400, a brake switching circuit 500, a brake light circuit 600 and a
manual brake circuit 700. All of these components are
interconnected by appropriate conductors, typically in the form of
traces on a printed circuit board to which the various circuit
groups are attached.
Central to the operation of the system is the microprocessor
circuit 20 which receives information from the accelerometer
circuits 200, the keypad circuits 300, the manual brake circuit
700, the brake switching circuit 500 and the stop light switching
circuit 600. Likewise, the microprocessor circuit 20 provides
signals which drive display circuits 400 and brake switching
circuits 500 and stop light switching circuits 600.
By way of overview, the power supply circuits 100 provide the
necessary amounts of current at appropriate voltages, to all of the
individual sub-circuits. The accelerometer circuits 200 sense
acceleration, and present raw acceleration data to the
microprocessor circuit 20. Manual brake circuit 700 accepts a
manual braking signal from the vehicle operator, and present
information regarding that braking signal to the microprocessor
circuit 20. Keypad circuit 300 accepts inputs from the vehicle
operator, and presents those inputs to the microprocessor 22 as
shown in FIG. 6. Microprocessor circuit 20 processes signals from
the microprocessor for human interface, and presents information
regarding the operation of the controller 10 to display circuits
400. Stop light switching circuit 600 accepts information regarding
a vehicle's stop lights and presents that information to
microprocessor circuit 20. The same circuit accepts information
from the microprocessor circuit 20 and conditions those signals for
output to the vehicle's brake light circuit. Brake switching
circuitry 500 accepts signals from the vehicle brake controls and
presents that information to microprocessor circuitry 20. Likewise,
microprocessor circuit 20 presents information regarding braking
computations and commands for braking to brake switching circuitry
500, which in turn, provides braking power output to the vehicle's
brakes.
Each of these sub-circuits will be discussed in detail in the
following sections. Typically, all of the sub-circuits and their
components are mounted to a single printed circuit board.
Power Supply
As shown in FIG. 3, power to the controller 10 is derived from a
power supply circuit 100 which employs reverse polarity protection
without sacrificing power loss. Normally, reverse polarity
protection schemes are accomplished utilizing diodes. However, even
the best diodes have some voltage drop. These voltage drops
generate heat in high current conditions. Therefore, many costly
diodes are usually required to handle reverse polarity protection.
In brake controllers of the type described herein, however, which
generates high output current, the use of conventional diode
reverse polarity protection is generally impractical. Instead, the
present circuit utilizes field effect transistors which operate in
parallel to protect the circuit without significant power loss.
As shown in FIG. 3, the vehicle in which the invention is used
normally supplies 12 volts at 70 or more amperes through positive
and negative inputs to the power supply. Typically, the source of
this power is the vehicle battery/alternator combination. A
transient voltage suppressor D1, such as a Fairchild SMCJ17CA is
connected across the positive and negative input to filter
transient voltages. This filtered input is then connected to FETs
Q1 and Q2. Current will not flow in the circuit unless the negative
input, i.e., the input connected to the drains of the FETs Q1 and
Q2 has a lower potential than the positive input, i.e., the voltage
provided to the gates. If the input power polarity is inadvertently
reversed, the circuit is essentially disabled. The net result is
fail-safe polarity protection without voltage drop or power
loss.
Accordingly, 12 volt power is presented to the stop light current
sensor U4 and brake current sensor U6. These are integrated circuit
packages which are essentially amplifiers which provide the
necessary high current required by the vehicle stop lights and the
vehicle brakes. Heavy traces are utilized on the outputs of sensors
U4 and U6 to carry the high currents generated thereby. The power
supply also includes conventional integrated circuit voltage
regulators U3 and U5 which provide carefully regulated output
voltages to power the main components of the system. The resistor
arrays RS11, RS12, and RS13, RS14 associated with each of the
voltage regulators U3 and U5 are selected to provide the necessary
resistances to the voltage regulators U3 and U5 to adjust the
voltage to the desired level. A typical installation incorporates
one or more filter capacitors arrays C19-C22 and C25-C28 associated
with the voltage outputs. Additionally, one or more capacitors C33
(and optionally C33-2 and C33-3) are utilized to stabilize the raw
positive input to the current sensors U4, U6 and voltage regulators
U3 and U5.
Similarly, voltage regulator U7 and associated circuitry R16, R17
and C34, C35 and C31 provides well-regulated 12.5 volts DC for use
by other elements of the controller circuit.
The power supply 100 thus generates well-regulated 5 VDC, 3.3 VDC
and 12.5 VDC outputs, as well as a conditioned, high-current 12
volt output for supplying 12 VDC power to the electronic brake
actuators and the vehicle stop light circuit.
Signals Interface Circuitry
FIG. 5A collects on one sheet the various signals interface
circuitry utilized by the invention. An accelerometer U14 is
powered by the power supply circuit 100, and provides a variable DC
voltage adjusted to 0-3.3v output. A graphical representation of
the output of the raw accelerometer output is depicted on the upper
graph trace A of FIG. 9. These acceleration/deceleration outputs
are conditioned by R31, C53 and R19, C36 and presented to
microcontroller U2. Hydraulic pressure sensing may be provided by
an optional pressure sensor (not shown) which provides a variable
output, which is conditioned by a circuit including one or more
Schottky barrier diodes D6, associated capacitor C37, and resistors
R20, R21 and R23. Typically, however, this sensing is used only for
initial calibration of the circuit during manufacturing and for
troubleshooting.
Similarly, the brake voltage output, voltmeter output, stop light
current meter output, brake current meter output, manual brake
button output, and stop light outputs are provided with comparable
conditioning circuitry in the form of one or more Schottky barrier
diode pairs D7, D8, D10, D11, and D30 and associated resistors and
capacitors. These outputs are fed to the microprocessor U2 (shown
in FIG. 6) and may be selectively displayed on display U1.
CPU Controller Circuitry
FIG. 6 represents the CPU controller circuitry, which is centered
on a commercially available microcontroller U2 such as the Zilog
Z8F series. The microcontroller U2 accepts inputs from the
accelerometer circuits 200, and the towing vehicle's brake light
circuitry, the manual brake operation circuits and a dedicated
array of signal inputs as depicted in FIG. 5A. The controller 10
provides output to one or more status indicators, such as a
multi-character alphanumeric display U1 or a graphic display U1A,
and provides a pulse width modulated output signal which, when
amplified, controls the braking function of the towed vehicle.
A typical microcontroller U2 adapted for this application is also
provided with a crystal X1 controlled clock circuit including R12,
C15 and C16 to provide the necessary timing signals. In one
embodiment, the microcontroller U2 maintains its own internal
read-only memory and random access memory, as well as
analog-to-digital converters, on-board timers, multiple
input/output ports and multiple universal asynchronous receiver
transmitter (UART) circuits. Power is supplied to the
multi-character display U1 and the microprocessor U2 by the system
power supply circuit 100 depicted in FIG. 3.
The brakes of the towed vehicle are thus electrically operated by
the controller 10. Operation of the towed vehicles brakes by the
controller 10 of the present invention may occur in one of two
ways: a) automatic brake operation responsive to vehicle speed,
angle of ascent or descent, and acceleration or deceleration or b)
"manual" brake operation, wherein the towed vehicle's brakes are
directly operated responsive to a variable input from the vehicle
operator independent of the operation of the towing vehicle's
brakes.
Manual Brake Operation
An understanding of the manual operation of the brake system using
hand switch 6 will best be understood with reference to FIG. 5,
FIG. 5A and FIG. 6. In FIG. 5A, the signals' interface circuitry,
the brake button potentiometer RP2 is depicted. RP2 is in the form
of a conventional potentiometer, the adjustment of which is under
manual control of the vehicle operator. The variable output of
potentiometer RP2 feeds, through resistor R40, an input of the
microcontroller U2. This input to the microcontroller U2 results in
an output from the microcontroller of a variable voltage which is
fed to the source of the stoplight driver U11 shown in FIG. 5. The
stoplight driver U11 of FIG. 5 is in the form of a high-side MOSFET
driver, the function of which is to provide the necessary voltages
to the FETs Q6 and Q7, which require higher voltages for operation
than other similar semiconductors. The input to the stoplight
driver U11 also is connected to an LED 2 which illuminates to
provide a visual indication that manual braking power is being
applied to the towed vehicle. The output of a driver U11 activates
FETs Q6 and Q7 which, together with their associated circuitry,
provide output to actuate the vehicle brake lights. Heavy traces
are used as depicted in this schematic to ensure that the
controller 10 has sufficient current carrying capability to supply
current to a large array of brake lights.
In a similar fashion, manual operation of the brakes produces a
brake output which is presented to the circuitry of FIG. 4. Brake
power for power supply circuit 100 is controlled by driver U8 and
switched by brake FETs Q3, Q4 and Q5, which collectively route
sufficient power to the electrical braking components of the towed
vehicle.
In the automatic braking mode, the occurrence of a braking event is
sensed as the brake pedal of the towing vehicle is depressed and
the brake light circuit in the towing vehicle is activated. As
depicted in FIG. 5, the towing vehicle's stop light power bus is
activated when the brake pedal is depressed. The presence of 12
volts on the towing vehicle's stop light bus is sensed by the
microcontroller U2, which initiates the braking action in the towed
vehicle according to a number of other input parameters.
The microcontroller U2 functions to sense the occurrence of a
braking event when the stop light output of FIG. 5A is energized to
12 volts. This output is conditioned by the stop light detect
barrier diodes D30 to generate an appropriate 3.3 volt output to be
sensed by the microcontroller U2.
Prior to and during the braking operation, the microcontroller U2
receives continuous input from the accelerometer U14 depicted in
FIG. 3. Accelerometer U14 is continuously providing data regarding
the x and y angle, acceleration and/or deceleration of the towing
vehicle in which the controller 10 of the present invention is
installed.
In the present invention, a principal feature is to provide
electronic brake output signals which correspond to the brake
signals being provided by the towing vehicle's hydraulic braking
system. In other words, it is desired that the force supplied to
the electronic brakes of the towed vehicle should correspond to the
force applied to the hydraulic brakes of the towing vehicle.
By creating a mathematical model of the desired braking action, it
is possible to precisely control the towed vehicle brakes. An
example of this methodology is depicted in FIG. 9, which is a graph
representing typical hydraulic brake force applications B, raw
accelerometer readings A and the resultant computed current output
C from the present invention to the magnetic brakes on the towed
vehicle.
The upper array of points on the graph reflects the raw inertial
values (from 0-3.3 UDC) produced by the accelerometer U14 in the x
axis during a straight-ahead stop.
The array of graph points B represents the pounds per square inch
of braking pressure being applied to the towing vehicle's brakes by
the operator of the towing vehicle.
An array of points designated C represents the actual electrical
braking power output produced by the present invention in response
to the braking event.
On the graphical representation of FIG. 9, the range of pressure
represented by the line B on the graph represents a typical fifty
(50) mile per hour stop and reflects hydraulic pressure per square
inch of between 0 and 2000 PSI. Corresponding to line C is the
calculated and corresponding electrical output from the controller
10, showing an amplified signal output between 0 and 4.5 volts. The
raw output of the accelerometer varies between 0 and 3.3 volts.
The present invention uses a well-defined algorithm to calculate
effective braking. During a non-braking condition, the algorithm
causes the microcontroller U2 to take readings from the
accelerometer U14 every ten milliseconds. These readings are stored
in an array in memory in the microcontroller. During a braking
event, accelerometer output readings are likewise taken every 1
millisecond and subsequently averaged every millisecond, and stored
in an array in memory in the microprocessor as depicted below:
##STR00001##
These stored values are utilized for calculating a trend line of
motion acceleration and deceleration of the vehicle. The array is
continuously updated with every reading, rotating the older
readings out of the array at the same time that newer readings are
stored. The values in the array are utilized as a basis for
computing the amount of electrical energy which must be imparted to
the brakes during the braking operation. By thus computing a moving
average acceleration value in advance of the braking event, a more
precise determination of actual braking requirements can be
determined during the deceleration process. For example, slower
average speeds during non-braking activity yields smaller braking
requirements during a braking event.
Pulse Width Modulated Braking
The present invention utilizes a pulse width modulated signal to
control trailer braking. It has been determined that a square wave
pulse width modulated signal generates an improved braking signal
as opposed to sinusoidal waves or flat voltages. It is desirable
that braking energy be applied to electric brakes in short bursts.
By regulating the width of the pulse of electrical energy supplied
to the magnetic brake actuator within the conventional electronic
brake, a smoother and better controlled braking operation is
insured. FIGS. 10-12 depict three typical braking signals which may
be applied utilizing pulse with modulation circuits. In FIG. 10, a
typical 13.7 volt automotive source voltage is applied to the
magnetic brake utilizing 1 millisecond duration per pulse. The net
effective voltage applied to the magnetic brakes is 0.69 volts
DC.
In FIG. 11, a longer duration signal is supplied, providing
effective voltage of 6.37 volts DC. In FIG. 12, the pulse width
duration is substantially longer, producing an effective voltage of
approximately 12.5 volts DC.
The amount of braking power generated by the controller is also
adjusted in relation to the measured performance of the electronic
brakes to compensate for brake overheating and fade as a result of
a higher frequency of brake application. It is well known that the
amount of current drawn by electronic braking systems varies with
the temperature of the electronic brake actuators. Accordingly, by
evaluating changes in current required by the braking actuators
under similar pulse width modulation duty cycles, the present
invention recognizes and adjusts subsequent brake output by varying
the pulse width modulated signal in response to the changing power
requirements of the brake electronic actuators. To further improve
the response of the controller to these varying power requirements,
software within the microcontroller periodically reevaluates
changes and duty cycle required by trends in braking power
utilized.
Main Process Flow
A better understanding of the functioning of the system will be
obtained by reference to FIG. 7, which is a flow chart outlining
the main process and control of the invention.
In the initialization step, which occurs automatically upon
power-up of the controller, the microprocessor initiates a start-up
routine which initializes the various timers, UARTs, display, pulse
width modulation and analog to digital controls circuits and
internal software.
The first operative step in the main loop process is the strobing
of the internal watchdog timer. Periodic strobing of the internal
watchdog timer is necessary to continue normal operation of the
microcontroller and associated circuitry without a system reset.
The watchdog timer is set to require a strobe signal every 100
milliseconds. If the watchdog timer determines that more than 100
milliseconds have passed without a strobe signal, the system
resets. In the event of a system reset, an error flag is set and an
appropriate message is reported by the controller 10, which is both
stored and presented to the controller display U1.
Assuming that the watchdog timer conditions have been met, the main
process continues to the pulse width modulation scan process,
wherein the microcontroller scans the inputs which determine
requirements for pulse width modulation output or steady state
braking output. If pulse width modulation braking is called for,
the pulse width modulation circuitry and software functions as
described herein in the pulse width modulation scan flow of FIG. 8
is implemented.
The next step in the main loop flow chart is illumination of the
"braking" light-emitting diode on the controller. Brake controller
10 is designed to be operative regardless of whether the vehicle in
which the controller 10 is located is operating with the
engine-driven electrical system generating power, and will operate
from the battery power of the vehicle in which they are installed,
to insure that the controllers will continue to operate the brakes,
regardless of whether the vehicle's engine is in operation, for
safety purposes. Because the brake controller of the present
invention utilizes a display utilizing a measurable, albeit small,
amount of electrical current, the circuits are designed to
extinguish the display after approximately 150 minutes of
inactivity. Even though the display is extinguished, however, the
controller continues to function.
The next step in the main loop process involves reading and
averaging values from the analog to digital converter hardware and
software within the microprocessor. The accelerometer provides a
continuous signal in the form of a varying voltage proportional to
the amount of acceleration or deceleration in a predetermined axis.
This information is fed to the analog to digital conversion
circuitry of the microprocessor, and software routines utilized by
the microprocessor convert the accelerometer signal to a digital
value which is then transferred to the accelerometer value array.
The utilization of the data from the accelerometer value array is
discussed in further detail, infra.
The next step in the main process is scan of the keypad inputs. The
controller is provided with one or more switches as part of a user
keypad which allows the user to select options for the operation of
the controller and the operation of the display. During each cycle
through the main process loop, the microprocessor scans to
determine whether or not any such user input has been received, and
if so, generates the necessary action responsive to the keypad
input.
The next steps in the main process flow are the initiation and/or
refresh of information to be displayed on the display provided on
the controller. The display is appropriately updated with data or
messages presented to the display by the microprocessor.
The final step in the main loop process is the error flag detect
and process step. Should any input to the microprocessor fall
outside predetermined specifications, an error flag will be set,
and an appropriate indication will be returned to the display.
The above-described main process loop continues for as long as
power is supplied to the system and no error flag remains set
assuming that the watchdog timer is appropriately strobed at least
every 100 milliseconds as above-described.
Braking Flow Chart
Each cycle through the main process loop visits a sub-process as
defined in the braking flow chart at FIG. 8.
The initial step in the braking process is a determination as to
whether or not the manual brake control has been activated. As
above explained, the manual brake activation button is in the form
of a potentiometer which provides a variable input to the analog to
digital converter within the microprocessor. Upon confirmation that
a manual brake input has been received, the processor sends a
signal to activate the vehicle stoplights, and immediately
thereafter updates the pulse width modulation value to a value
corresponding to the proportionate amount of braking which has been
selected by the manual brake potentiometer. Once the correct pulse
width modulation has been established by this process, a signal is
sent to the brake switching circuitry in the form of a pulse width
modulated signal, which is converted to a higher power pulse with
modulated output which causes the electric brakes on the vehicle to
function in appropriate proportion to the amount of deflection of
the manual control.
An alternative step in the braking flow process, in the event of a
determination that the manual brake control has not been operated,
is to determine whether or not the vehicle stop lights are on. It
is the operation of the vehicle stop lights which trigger the
remaining steps in the braking process. If the microprocessor
determines that the stop lights are not illuminated, the braking
process flow simply stores the current accelerometer non-braking
values in an array within the microprocessor memory,
simultaneously, the oldest stored values in the array are
discarded. In this fashion, the microprocessor acceleration value
array is continuously updated with vehicle acceleration data. After
updating the array as described, the braking flow process is
completed and the operation of the microcontroller returns to the
main process loop.
If the braking process software determines, however, that the
vehicle stop light is on, the braking flow process then calculates
an appropriate pulse width modulation signal utilizing the data
contained in the accelerometer value array.
To obtain the most precise pulse width for optimal braking, a
mathematical algorithm is utilized in the software to calculate the
appropriate brake output signal.
At all times while the controller is operational, accelerometer
readings are taken at 1 millisecond intervals. When no braking
signal is being supplied to the controller, a non-braking slow
moving average is calculated, creating a non-braking slow moving
average utilizing the immediate accelerometer reading and some
multiple of prior accelerometer readings in a non-braking
situation.
When the brakes are applied, a braking moving average is calculated
utilizing the immediate raw accelerometer readings minus the
non-braking moving average. This result is multiplied by a constant
stored in the accelerometer value array. The value so computed
replaces the oldest value in the array, so that, at any given
instant during a braking event, the accelerometer array contains
the most recent twenty braking moving average values. Once the
value has been stored in the array, the entire array is averaged to
establish a single calculated brake output value. This calculated
brake output value is used to establish the precise amount of power
to be applied to the brakes.
By utilizing all non-braking activity to generate a moving average
acceleration value, and then using this value to calculate braking
rates during the deceleration process, it is possible to remove the
jerkiness or abbreviated stopping normally associated with simple
inertia-based brake controllers.
* * * * *